This application relates generally to distributing the load demand between servers on a network, and, more specifically, to employing an HTTP cookie to balance the load demand between servers on a wide area network of geographically distributed servers such as the Internet.
Generally, it has proven difficult to reliably and efficiently load balance the demand for access to resources, e.g., a web-based application, email and streamed multimedia data, on a wide area network (WAN). One prior art attempt employed a look up table for storing a relationship mapping between a client""s ip address and the ip address of the actual server that provided access to the resources for a domain name/ip address request. This table was usually held in the memory of a server array controller that managed several node servers that could provide access to the resources associated with the client""s request. Typically, the server array controller would employ a load balancing technique to select and map the ip address of one of the managed node servers to the client""s actual ip address and store this mapped relationship with a time stamp in the table. In this way, when a client repeated an request before the expiration of the time stamp, the controller would use the mapping stored in the table to automatically connect the client to the previously selected (load balanced) node server.
Additionally, if the time stamp had expired, the server array controller would again perform the load balancing technique to select one of the managed node servers to provide the actual access to the resources associated with the request. Each time the load balancing technique was performed, the controller would update the table to include a new time stamp and a new mapping of the client""s unique ip address to the currently selected node server""s ip address.
For a relatively small number of client requests, the above described prior art solution could reduce the demand on server array controller resources because the controller did not always have to perform a load balancing technique for each client request that occurred before the expiration of the time stamp. Instead, the controller only performed the load balancing technique for a new client request or when the time stamp for a previous client request was expired. However, since all of the table entries had to be kept in the memory of the server array controller to be used effectively, the available controller resources for load balancing and managing several node servers decreased in proportion to an increase in the number of client requests. To ensure that table entries were not lost when the server array controller lost power or was rebooted, a copy of the table would be stored on a secondary storage medium. Also, under heavy load conditions, the secondary storage medium was often not fast enough to store the copy of table entries before the server array controller shut down.
Another significant problem with the prior art approach was that the client""s ip address was not always unique. Although some clients might have their own unique ip address, many others used random virtual client ip addresses provided by a large Internet Service Provider (ISP), e.g., the America On-Line Corporation, to connect to the Internet. Since only a portion of a large ISP""s clients are typically connected at any one time, a large ISP usually employs a proxy cache to randomly assign a relatively small number of virtual client ip addresses to the currently xe2x80x9con-linexe2x80x9d (customers) clients. Typically, a proxy cache will assign one of the virtual client ip addresses to a client on a first available basis each time the client connects to the ISP and starts a session on the Internet. From the discussion above, it is apparent that when a client used a large ISP to connect to a WAN such as the Internet, the prior art did not provide an effective method for persistently mapping a client""s relationship to the server that was selected to provide access to resources associated with a request.
Therefore, it is desirable to provide a method and system for automatically providing a persistent mapping of a previously selected destination for a domain namer ip address request. Preferably, the present invention employs a Cookie in a Hyper Text Transport Protocol (HTTP) data stream to identify a relationship between a previously selected destination and a client""s HTTP request. The present invention overcomes many of the limitations of the prior art caused by the direct mapping of an actual destination ip address to a client""s ip address.
In accordance with the present invention, a method for load balancing access to a resource identified in an HTTP request. The method includes: (1) examining an HTTP request to determine when a Cookie is included with the HTTP request, the Cookie may include information that indicates a destination for accessing the resource identified in the HTTP request; (2) when the Cookie is included in the HTTP request, sending the HTTP request to the destination that is indicated by the Cookie""s information; (3) generating an HTTP response at the destination, the HTTP response providing access to the requested resource; (4) inserting a copy of the information in the Cookie; and (5) sending the HTTP response with the copy of the information in the Cookie to the sender of the HTTP request, so that a subsequent HTTP request to access the resource will include another Cookie with information indicating that the resource is accessible at the destination.
In accordance with other aspects of the present invention, the method provides for sending the HTTP request to a server array controller that manages a plurality of node servers. The server array controller selects one of the plurality of node servers to receive the HTTP request based on the information in the Cookie. The selected node server is associated with the destination and generates the HTTP response that includes the copy of the information in the Cookie.
In accordance with yet other aspects of the present invention, the method provides for including an identifier with the copy of the information in the Cookie. The identifier associates the selected node server with the destination. The identifier may be encoded by a mathematical product such as a hash value. Also, a time stamp may be generated by the node server, server array controller or any network transmission device and included in the HTTP response.
In accordance with additional aspects of the present invention, the method provides for employing a selected node server to generate the HTTP response and includes a blank identifier in the copy of the information in the Cookie. In this case, the server array controller may write the identifier over the blank identifier in the copy of the information in the Cookie. The method may also provide for changing an expiration date for the time stamp relative to the number of HTTP requests sent to the server array controller over a period of time. The expiration date for the time stamp can be increased when the number of HTTP requests sent to the server array controller are greater than a determined value over a period of time. Alternatively, the expiration date for the time stamp may be decreased when the number of HTTP requests sent to the server array controller are less than a determined value over a period of time.
In accordance with other aspects of the present invention, the method provides for employing the server array controller to select one of the plurality of node servers to receive the HTTP request and generate the HTTP response providing access to the requested resource when the Cookie is not included in the HTTP request. The present invention provides for sending an HTTP response to the sender of the HTTP request with information for creating another Cookie, so that a subsequent HTTP request to access the resource will include the other Cookie with information indicating that the selected node server is the destination for accessing the requested resource.
In accordance with still other aspects of the present invention, the method provides for employing the server array controller to balance the load demand on the plurality of node servers by determining the optimal node server to receive the HTTP request and generate the HTTP response. The server array controller may employ one of a plurality of functions to determine the optimal node server to balance the load demand. These functions include round trip time, round robin, least connections, packet completion rate, quality of service, server array controller packet rate, topology, global availability, hops, static ratio and dynamic ratio.
In accordance with additional aspects of the present invention, until the HTTP request is provided to the server array controller, the method provides for employing the server array controller to buffer communication between the sender and the destination. Also, when the HTTP request is provided to the server array controller, replaying in consecutive order the buffered communication to at least one of the plurality of node servers that is associated with the destination.
In accordance with other aspects of the present invention, a plurality of Cookies may be included with the HTTP request. Each Cookie can have a different type that indicates how the information included in a Cookie is to be utilized. The different types of Cookie include priority, path and hops. The path type of Cookie includes information indicating all of the interim destinations between the sender and the destination for an HTTP request. The interim destinations include a router, host machine, server array controller, firewall, node server and client. The hops type of Cookie includes information indicating a portion of the interim destinations between the sender and the destination for an HTTP request. The priority type of Cookie includes information indicating when the HTTP request and/or response associated with the Cookie is to be processed prior to the processing of other HTTP communications. The priority type of Cookie may include an indication that identifies a priority for processing the HTTP request and/or response prior to the processing of the other HTTP communications.
In accordance with yet other aspects of the present invention, wherein the sender may include a client, server and host machine. Also, the destination can include a host machine, server array controller, router, node server, firewall and client.
In accordance with the present invention, another method for load balancing access to a resource identified in an HTTP request, comprising: (1) examining an HTTP request to determine when a Cookie is included with the HTTP request, the Cookie including information that identifies a sender of the HTTP request; (2)
when the Cookie is included in the HTTP request, comparing the information identifying the sender to a table of at least one destination, the HTTP request being sent to a destination that is associated with the identified sender in the table; (3)
generating an HTTP response at the destination, the HTTP response providing access to the requested resource and including a copy of the information in the Cookie; and (4) sending the HTTP response with the copy of the information in the Cookie to the identified sender of the HTTP request, so that a subsequent HTTP request to access the resource from the identified sender will include another Cookie with information that identifies the sender of the subsequent HTTP request.
In accordance with other aspects of the present invention, the other method provides for employing a server array controller that manages a plurality of node servers. The server array controller comparing the information identifying the sender to a destination that is associated with the identified sender in the table. The destination can be one of the node servers managed by the server array controller.
In accordance with yet additional aspects of the present invention, a system which implements substantially the same functionality in substantially the same manner as the methods described above is provided.
In accordance with other additional aspects of this invention, a computer-readable medium that includes computer-executable instructions may be used to perform substantially the same methods as those described above is provided.